In U.S. Pat. No. 3,981,481 granted Sept. 21, 1976, assigned to the same assignee as the present application, a bottom operable tank car valve is disclosed including a valve body attached to an opening in the bottom of the tank. The valve body includes an opening centrally thereof for loading and unloading the lading. A depending housing is attached to the valve body with mechanical fasteners which constitute a shear plane. The housing includes a loading and unloading spout extending radially outwardly from the outlet. An operating assembly for loading and unloading the tank is mounted within a bore in the lower portion of the housing. The operating assembly includes a lower operator which extends below the valve housing and which is adapted to be engaged by a suitable unloading tool. The lower operator has a square opening engaging with clearance a square head on an upper valve operator which extends upwardly within the opening in the valve body. A retainer assembly attached to the valve body maintains the upper operator vertically fixed and spaced from the walls of the valve body. The upper operator engages a depending member from a valve closure. The closure is movable between a closed position engaging the top surface of the retainer assembly, and an open position to load or unload the lading.
In accordance with one embodiment in the '481 patent the upper operator engaging the depending valve closure is located within the valve body at a point above the shear plane defined by the mechanical fasteners holding the housing in engagement with the valve body (FIGS. 10 and 11 of the '481 patent). Thus in the event of impact to the depending housing, the housing will shear off along the shear plane provided in the mechanical fasteners, and the lower operator will drop off, leaving in place the upper operator within the valve body. After such an impact the car can be unloaded by attaching a suitable tool to the head on the upper operator to raise the valve closure and unload the car.
While this arrangement is considered to be highly advantageous in protecting the car against impacts bursting the tank, it does have some disadvantages. If in transit or during derailment the lower portion of the valve housing is impacted, some of the impact force is transmitted to the lower operator, and then upwardly into the upper valve operator. This force may result in damage to the upper operator such as deforming and rendering inoperative the threads for moving the valve closure vertically, or forcing the upper operator upwardly and moving the valve closure out of the closed position, causing lading to come out of the tank. This problem is more serious if the operator neglects to replace a removable cap on the valve housing, which provides some protection against impacts to the lower housing and/or operating assembly being transmitted up into the second operator and valve plug.
Thus it would be desirable to provide a bottom operable loading and unloading valve assembly in which impacts to the lower portion of the housing and valve assembly are less readily transmitted vertically up into the upper operator and into the valve plug.
If the operating assembly for opening the valve is damaged in transit, expensive operator time is required at the unloading site to repair the outlet prior to its unloading. This results in reduced unloading rates and may require the car be taken out of service for repairs.
Furthermore, the depending valve housing is a heavy and expensive member, usually a casting. If this housing could be eliminated, or made smaller, considerable cost and weight savings in the tank car valve assembly would be obtained. Also, the size and weight of this housing makes disassembly and removal of the housing awkward for the operator.
Usually the spout for unloading on the housing extends radially outwardly from the outlet only in one direction. This requires that the unloading operator move the unloading hose and connection adapter so as to engage the unloading spout in the position that the spout is located when the car arrives at destination. Since the unloading hose is often heavy and often includes little surplus length, this can be a difficult operation, and may require relocation of the tank car.
The present housing requires that the unloading hose be attached with a threaded connection. Threads are provided on the housing for attaching the unloading hose and for attaching a removable cap which is applied over the loading and unloading spout. Some receivers prefer to attach the unloading hose to the internal threads where the unloading plug is attached and where the tube for heating congealed lading is usually attached (element 104, FIG. 1 of the '481 patent). In either case attachment of the unloading hose to a threaded fitting may require the cost of the expensive plummer time in some locations to make this connection. Thus a quick-connect-disconnect connection would be more desirable than the threaded connections presently provided on the housing.